The present invention is directed to a capacitor discharge ignition system having in-phase charge, trigger and shut-off coils. In addition, the system may provide force commutation of the electronic switch, independent variation of three triggering circuit characteristics dependent on the selection of component value, compensation for temperature variations, inhibition of extraneous gating of the electronic switch, and engine shut-off.
Capacitor discharge ignition systems are well known in which a flywheel magnet is rotated into and out of flux cutting proximity to one coil effecting charging of an ignition capacitor and to another coil for effecting the triggering of an electronic switch discharging the ignition capacitor through a high voltage transformer to a gap ignition device of the engine. The necessary temporal displacement between the charging of the ignition capacitor and the triggering of the electronic switch is generally achieved by the physical displacement of the charge and trigger coils, or the winding thereof in opposite directions to provide out-of-phase waveforms. Since space is at a premium in many applications, the physical displacement of the coils may be unsatisfactory and the winding of out-of-phase coils generally includes additional manufacturing steps.
It is accordingly an object of the present invention to provide a novel method and capacitor discharge ignition circuit which utilized inphase trigger and charge coils wound on the same core in the same direction to reduce manufacturing steps.
The problem of false gating, i.e., gating at undesirable times as a result of transients such as exist upon the cessation of the charge coil waveform, has typically been addressed by the utilization of a capacitor which absorbed the transients and therefore isolated the gate electrode therefrom. However, the use of an expensive capacitor for this purpose also results in the absorption of power from the trigger coil necessitating the use of a larger trigger coil.
It is another object of the present invention to provide a novel method and capacitor discharge ignition circuit which reduces false gating in response to transients without an increased trigger coil power output requirement through the utilization of a more stable and less expensive triggering and bias circuit for the electronic switch.
Capacitor discharge ignition circuits find many applications in hostile environments such as in construction sites and in logging operations where they are often exposed to a wide range of ambient temperature as well as the heat generated by the widely varying loads on the engines with which they are associated. The holding current, i.e., that required to maintain switch conduction, and the sensitivity of the switch are generally independently responsive to such changes in temperature.
It is still another object of the present invention to provide a novel method and capacitor discharge ignition circuit having improved temperature stability while achieving improved design flexibility by maintaining independent control over gate sensitivity, gate current and the degree of back bias of the electronic switch.
Conventional capacitor discharge ignition systems may employ a manual shut-off switch to ground the connection between the trigger coil and the gate electrode of the electronic switch to prevent discharge of the ignition capacitor. A potential consequence of this shut-off method is, as a result of the continued rotation of the flywheel magnet in proximity of the charge coil due to the inertia of the engine, a continued build-up of the charge on the ignition capacitor to a voltage sufficient to cause breakdown of the capacitor or of the electronic switch. An alternative known method involves the shorting of the charge coil by a manually operable switch. However, a significant potential of arcing occurs.
It is a further object of the present invention to provide a novel method and capacitor discharge ignition circuit which achieves engine shut-off by shorting the trigger coil while at the same time reducing the charge coil potential by loading the core and thus limiting the magnitude of the charge which accumulates on the ignition capacitor.
Capacitor discharge ignition systems have achieved force commutation of the electronic switch by means of the spark current. However, such a design requires that only a single pulse, unidirectional spark current be employed.
It is yet another object of the present invention to provide a novel method and capacitor discharge ignition circuit which achieves force commutation with a multiple pulse, bidirectional spark.
Heavily loaded trigger circuits are known to be advantageous because of temperature stability, transient suppression, etc. but excessive current results at high engine speed to the detriment of the expensive electronic switch.
It is yet still another object of the present invention to provide a novel method and capacitor discharge ignition circuit which provides protection for the electronic switch despite wide variations in the generated trigger circuit power as a result of engine speed.
These and many other objects of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description when read in conjuction with the appended drawings.